1. Field of the Invention
The invention relates to a washing machine or washer-dryer provided with a drum mounted for horizontal or inclined rotation within a suds basin and provided with a cylindrical wall and two end plates, the cylindrical wall or one of the end plates being provided with a removal opening and the cylindrical wall being made completely or in part of sheet metal texturized with bulges facing the interior of the drum.
2. The Prior Art
Drums for automatic washers or washer-dryers usually consist of sheet metal structures. Owing to high spinning speeds of up to 1,600 rpm the drums are subject to stringent requirements as regards their strength, dimensional stability and rigidity. From German patent 4,437,986 A1 and laid-open specification 2,557,215 it is known to texturized the sheet metal from which the drum is to be made with bulges in order to increase its strength.
Furthermore, it is conventional in washing machines to provide perforations in the cylindrical wall as well as, if necessary, in the end plates to ensure an exchange of suds between the laundry and the suds basin. In present day washing machines these perforations have a diameter in the order of 3.5 mm. To this end, during manufacture of the drum holes with a diameter of about 2.5 mm are initially punched into a sheet metal coil and are thereafter deepened to a funnel shape and flared to 3.5 mm, by an embossing process known as drift punching. When shaping and welding a cut coil section into a cylindrical wall the recesses of the holes are directed towards the outside. This is done to ensure that no burrs at the edge of any hole protrude into the interior of the drum, thus to prevent contact between the laundry and such burrs. Drift punching and the resultant structure of the inner surface of the drum results on the one hand in a reduced planar surface relative to the overall cylindrical surface and, on the other hand, in diffuse reflection of light falling into the drum. This not only creates an impression of high quality and gloss, that is to say of high-grade material, but it also suppresses the visibility of scratches and impurities.
A washing machine is known from U.S. Pat. No. 2,591,143 the drum of which is provided with a bulging texturization structured as corrugations extending over the entire length of the cylindrical wall of the drum. In this arrangement, the perforations of the drum are disposed within the outwardly facing recesses. His leads to residual water remaining in the planar sections between the holes and to impeding drainage. Moreover, such a drum structure leads to excessive abrasion and, hence, damage of the laundry.
In connection with the mentioned drums it has been found to be disadvantageous that the relatively large perforations are the cause of burls in fabrics, damaged laundry and undesirable passage of threads and foreign matter. For this reason, it has been proposed to reduce the diameter of the holes (German laid-open specification 1,410,985) and/or to restrict the perforations to certain areas of the cylindrical wall (German patent 2,826,506).
To obtain drift punched holes of a 2 mm diameter, the diameter of the punching tools must not exceed a maximum diameter of about 1.2 mm. The gauge of the sheet metal customarily used for washing machine drums would quickly lead to breaking of the tools. For that reason, it is not possible to manufacture washing machine drums with drift punched holes in an automated fabrication process.
Drums with hole diameters of about 2 mm which have not been drift punched thus have a relatively smooth surface which lacks the previously described optical property. This is also true of drums perforated in partial areas as the non-perforated sections of their cylindrical wall are completely smooth. Moreover, another drawback of such drums is that residual water will remain on the smooth surface and impedes drainage.
It is, therefore, an object of the invention so to structure the drum of a washing machine that it provides a good visual appearance as well as complete drainage of residual water.
In accordance with the invention the object is achieved by drum washing machines wherein at least the cylindrical surface of the drum is texturized with a plurality of bulges of polygonal configuration facing the interior of the drum and forming between them marginal contours extending towards the exterior of the drum and wherein holes are provided in the marginal contours at the corner points of the polygons;
Aside from solving the aforementioned problems, the advantages to be derived from the invention reside in increased stability of the drum. This allows reduction of the costs incurred by the use of heavy-gauge sheet metals or complex forming processes (e.g. expanding). Alternatively, the safety space between the drum and the suds basin which during spinning serves to prevent contact between drum and suds basin may be reduced while maintaining given sheet metal gauges. In this manner, the so-called dead space between the wall of the drum and the wall of the suds basin is reduced, i.e. the quantity of free suds is reduced (low water and energy consumption) and the volume of the drum may be enlarged. Structuring the bulging texturization as polygons facing the interior of the drum and placing the holes at the corner points of the marginal contours results in a pattern of the bulging texturization which can be manufactured relatively easily and, in addition, the holes are disposed at the lowest points which leads to a significant improvement in the drainage of the washing suds and of the rinsing water, as the case may be.
In another inventive embodiment of the drum washing machine according to the invention the holes are disposed in sections of the cylindrical wall which are free of any bulges. Such a drum facilitates perforating as the perforations need not conform to the configuration of the bulges. The holes may be arranged in marginal sections bordering on the end surfaces (cap, bottom) or in the center portion of the cylindrical wall.
It is also advantageous to provide the marginal contours with a flat portion extending in the circumferential direction of the cylindrical wall of the drum and to place the holes in this portion. In the manufacturing process described elsewhere (page 1, line 23 to page 2, line 1) structuring and stabilizing contours are embossed by expanding into the perforated cylindrical wall. Thereafter, it is provided with a texture of bulges by a process known from German patent 4,437,986 A1 or German laid-open specification 2,557,215. Such a process makes it impossible to punch perforations into the wall of the drum which has already been rounded and provided with the texture of bulges. It is relatively difficult vertically to align the perforations punched into the sheet metal coil and the bulges of the texture made by expanding the circular wall such that the holes are located precisely at the corner points of the bulging structure. Changing the sequence of the manufacturing steps to a process in which the structure is formed before it is perforated is also unsatisfactory in terms of manufacturing techniques since the bulging structures may become damaged by the perforation. Broadening the marginal contours enlarges the tolerance range in which the holes are to be placed so that perforating by an automated production process is simplified. This is particularly true where the width of the flat portion measures one and a half to two and a half times the diameter of a hole.
It is also advantageous to reduce number and diameter of the holes relative to those of conventional drum washing machines. This leads to a reduction in the passage of lint or threads and to a gentler treatment of the laundry.